[Digestion] Use of centrifugal pump for transferring feedstock into digester

Sat Nov 16 20:22:38 CST 2013

Centrifugal pump works fine for us here on a 1000 M³ digester. Maintain the pump below the level of the holding tank to minimize air entry. We do incorporate about 35% liquid digestate from the digester into the new incoming slurry - before the pump. 

Date: Sun, 17 Nov 2013 07:35:33 +0530
From: adkarve at gmail.com
To: davidf at kingdombio.com; digestion at lists.bioenergylists.org
Subject: Re: [Digestion] Use of centrifugal pump for transferring feedstock into digester

Dear Dr. Fulford,
thanks a lot for the explanation and the solution.
Yours
A.D.Karve

On Sun, Nov 17, 2013 at 12:45 AM, David <davidf at kingdombio.com> wrote:

Dr Karve and listers, Hello,

Tests I tried in a laboratory which involved pumping material into a digester suggested that flow velocity is important. The microbes do not seem to like being accelerated, and stop working. A centrifugal pump works by accelerating the fluid, so is not really suitable for use in an anaerobic digester. The type of pump most often used is a progressive cavity pump, although an archimedes screw is also good. 

Unfortunately, the project was not properly written up, mainly because it did not produce biogas. I did try to write a patent on the idea, but as it did not work, it became rather pointless. 

Best wishes,
David
davidf at kingdombio.com

******************************************************
Dr David Fulford CEnv MEI, 15, Brandon Ave, Woodley, Reading RG5 4PU

       Tel: +44(0)118 969 5039 Mob: +44(0)7746 806401
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------ Original Message ------
From: "Anand Karve" <adkarve at gmail.com>
To: "For Discussion of Anaerobic Digestion" <digestion at lists.bioenergylists.org>
Sent: 16/11/2013 07:35:15
Subject: Re: [Digestion] Use of centrifugal pump for transferring feedstock into digester

Dear Marc, 
the feedstock is going into the digester all right. So obstruction in the feed line is not the problem. 
Yours
A.D.Karve

On Sat, Nov 16, 2013 at 8:04 AM, Marc de Piolenc <piolenc at archivale.com> wrote:

There are at least two other possibilities

- cavitation within the pump leading to loss of "prime"; this is heavily dependent on where the pump is installed, bends and constriction in the feed line and so on

- formation of gas bubbles in the feed; why wouldn't fermentation start in the feed, given the right conditions? Those gas bubbles will act just like water vapor (cavitation) or air intrusion, and make the pump lose its "prime."

The usual remedy is installing a manual, reciprocating pump in line with the centrifugal pump. This is used for initially priming the centrifugal pump and for re-priming it if it gets gas-locked or "sucks dry." Whether this will work with a relatively thick slurry or not, I don't know.

Marc de Piolenc
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Dr. A.D. Karve
Trustee & Founder President, Appropriate Rural Technology Institute (ARTI)

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for more information about digestion, see
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and the Biogas Wiki http://biogas.wikispaces.com/ 		 	   		  
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